Mixed resolution printing for colour and monochrome printers

Abstract: A printer (10) with mixed base resolution capabilities, having a higher resolution monochrome component such as black and lower resolution components such as cyan, magenta and yellow. The different resolution components are integrated into the same printing mechanism for composite printing of higher resolution black and lower resolution color at the same time. For increased throughput, a higher resolution black printhead (98) has a wider swath.

Description: RELATED APPLICATIONS This application is related to copending application docket 1093752-1 filed as U.S. Serial No. 08/145367 on October 29, 1993 in the name of Gary M. Nobel, et al. entitled INTERCONNECT SCHEME FOR MOUNTING DIFFERENTLY CONFIGURED PRINTHEADS IN THE SAME CARRIAGE, which application is assigned to the assignee of this application. This application also relates to the following copending applications which are commonly owned by the assignee of this application, and which are incorporated herein by reference: ELECTRICAL INTERCONNECT SYSTEM FOR A PRINTER filed as Serial No. 08/56,345 on April 30, 1993 in the names of Arthur K. Wilson, et al. (corresponding to EP-A-622 253); MODULAR CARRIAGE ASSEMBLY FOR AN INKJET PRINTER filed as Serial No. 08/55,618 on April 30, 1993 in the names of Arthur K. Wilson, et al. (corresponding to EP-A-622 240); WIPING STRUCTURE FOR CLEANING ELECTRICAL CONTACTS FOR A PRINTER AND INK CARTRIDGE filed as Serial No. 08/56,009 on April 30, 1993 in the names of Corrina A. E. Hall, et al. ; METHOD AND DEVICE FOR PREVENTING UNINTENDED USE OF PRINT CARTRIDGES filed as Serial No. 08/56,961 on May 3, 1993 in the names of Jeffrey A. Thoman, et al. (corresponding to EP-A-623 471); SIDE BIASED DATUM SCHEME FOR INKJET CARTRIDGE AND CARRIAGE filed as Serial No. 08/57,241 on April 30, 1993 in the names of David W. Swanson, et al. (corresponding to EP-A-622 208); and PRINTHEAD WITH REDUCED INTERCONNECTIONS TO A PRINTER filed as Serial No. 07/958,833 on October 8, 1992 in the names of Michael B. Saunders, et al. (corresponding to EP-A-0592221). BACKGROUND OF THE INVENTION This invention relates generally to printers, and more specifically to printing devices and techniques for monochrome and color printers capable of achieving high quality resolution. High quality printers are typically characterized by numbers indicating their resolution in dots per inch (dpi). This resolution is usually described in the context of a two dimension coordinate system where one number indicates the resolution in the x-axis (as used herein, x-axis means the carriage scan axis for a swath printer), and another number indicates the resolution in the y-axis (as used herein, y-axis means the media advance axis for a swath printer). Thus, a resolution of 300/300 dpi generally indicates a carriage-scan axis resolution of 300 dots per inch and a media-advance axis resolution of 300 dots per inch. The resolution of a printhead is primarily determined by the actual printout dot size as it appears in a printout. So in the ideal theoretical world, a 300 dpi printhead is presumed to produce a printout dot size which is approximately 1/300th inch in diameter. But various common language usages have developed which define resolution in other closely related terms. For example, a printhead's resolution is often identified by its nozzle pitch (i.e., the distance between adjacent nozzles on a printhead), and a print mode resolution is often identified by its pixel addressability (i.e., the distance between adjacent pixels in a printout). There are several print mode techniques for expanding the print quality characteristics of a printhead. For example, a 1/300th inch nozzle pitch printhead could be used to create a 600 pixel/inch printout in the media-advance axis by changing the incremental advance distance of the media at the end of a swath and then employing a multi-pass print mode. As another example, a 1/300th inch nozzle pitch printhead could be used to create a 600 pixel/inch printout in the carriage scan axis by increasing the firing frequency of the printhead and/or changing the carriage scan speed. However, implementing these different print modes is rather complicated and requires sophisticated programming techniques, precisely engineered mechanical parts, and many circuit components. Moreover, the print quality of a lower resolution machine which has a 300 dpi addressable print mode is not as good as the print quality of a true 600 dpi resolution machine where both smallest dot size and addressability are each equal to 600 dpi. JP-A-05 261 941 describes an ink-jet recording head which prints black dots which are larger than colour dots, a black printhead having a lower resolution than the colour printhead. WO-A-91 089 02 discloses a printhead where the vertical spacing of the black orifices is less than the vertical spacing of colour orifices. During composite printing, when both black ink and colour ink are to be deposited on the same media, every other black orifice is used so that both black and colour are printed at the same vertical resolution. JP-A-61 104 856 describes an ink-jet printer which permits simultaneous printing of colour images without reducing printing speed of black characters, in which the printhead is provided with more black ink nozzles than colour ink nozzles. WO-A-90 029 25 describes a dual mode ink-jet printer for either high quality or high speed printing. The spacing between the nozzles in the colour ink arrays is greater than the spacing between the nozzles in the black ink array. BRIEF SUMMARY OF THE INVENTION It is a primary object of the invention to incorporate multiple resolution capabilities directly into the printer printheads in order to expand the capabilities of the printer to achieve high quality printing as well as greater throughput. A related object is to decrease research and development costs as well as decrease the time for bringing higher resolution printers to market. The present invention is defined in the appended claims. A feature of the invention is to provide a printer having higher base resolution for its black printing component and a lower base resolution for its color printing components such as cyan, magenta and yellow. A related object is to integrate both of the aforesaid black and color printing components into the same printing mechanism in order to provide composite printing of higher resolution black and lower resolution color at the same time. Another important feature of the invention is to provide increased throughput for the higher resolution monochrome component of the color printer. In the preferred form, a wider swath monochrome printhead such as a high resolution black printhead which produces approximately 600 dpi sized printout dots is mounted on the same carriage as narrower swath color printheads such as lower resolution cyan, magenta and yellow printheads which produce approximately 300 dpi sized printout dots, with the wider swath black printhead having overlapping printing alignment with all of the narrower swath color printheads. The wider swath black printhead has a 300 nozzle swath with a nozzle pitch of 1/600th inch to create a swath of approximately one-half inch, and the narrower swath color printheads each have a 100 nozzle swath with a nozzle pitch of 1/300th inch to create a swath of approximately one-third inch. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a typical inkjet printer which can incorporate the apparatus and method of the present invention; FIG. 2 shows a carriage having removable multi-color print cartridges, which can incorporated the apparatus and method of the present invention; FIG. 3 shows an exemplary lower resolution color inkjet print cartridge used in a presently preferred embodiment of the invention; FIG. 4 is a perspective view of a carriage incorporating presently preferred embodiment of the invention in an inkjet printer; FIG. 5 is a top view of the carriage of FIG. 4; FIG. 6 is a fragmentary view of the flex-circuit interconnect on the carriage of FIGS. 4 and 5, with the interior carriage walls cut away; FIG. 7 is a schematic block diagram of the presently preferred embodiment of the invention; FIG. 8 is a schematic bottom view as seen looking up from the media showing the alignment relationship of the nozzle arrays of FIG. 7; FIG. 9 is a schematic view showing the use of a foam member for operatively connecting a flex-circuit to a higher resolution black inkjet cartridge; FIG. 10 is an exploded view showing a flex-circuit frame portion of a carriage, with the foam spring member of FIG. 9 for assuring pressure connection of a flex-circuit to a higher resolution black inkjet cartridge, and a metal spring member for assuring pressure connection of a flex-circuit to lower resolution color inkjet cartridges; FIG. 11 is a front view of the flex-circuit frame of FIG. 10; and FIG. 12 is a schematic diagram showing the relative resolution between a 600 dpi printout of the black printheads and a 300 dpi printout of the color printheads of a presently preferred embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In a multiple pen printer, it is important to improve the output quality of a printed page and increase the speed at which that output can be obtained as economically and simply as possible. In a printer mechanism, the output quality of a printed page is a function of printhead resolution. The higher the resolution the better the print quality. Also, in a swath printer employing a scanning carriage, the speed at which the output can be obtained is a function of the width of the swath which is covered by the printhead. In current multi-pen printers, each pen has the same resolution and usually the same swath width. This means that all the supporting structure, mechanics and electronics needs to be scaled up to support the resolution of the entire set of pens. All this hardware is more expensive than the hardware to support a multi-resolution, multi-swath width pen set where one pen is at the higher resolution and larger width that is desired and the other pens in the set are at a lower resolution and smaller size. This invention provides the benefits of a higher resolution, larger swath pen in lower resolution, smaller swath pens in the same printing machine. The higher performance pen can be used to improve output quality by enhancing certain key features that appear frequently in a printed page such as text. Such a pen also improves thoughput by being able to print these frequent features faster. The other lower performance pens can be used for less frequent or less demanding features such as graphics. In the presently preferred embodiment of the invention disclosed herein, we have combined a 600 dpi 1/2 inch swath black pen with three 300 dpi color pens each generating a swath of approximately 1/3 inch. The high performance black pen is typically used for printing text and other "black only" features, and thus the output quality and throughput of these features is greater. It also improves the output quality of color graphics and color features by teaming with the three lower performance color pens when printing color graphics or color features. The black component of the graphics which is often a large portion of color graphics content is at a higher resolution and thus at a higher output quality level. The larger swath can then be combined with printing algorithms to improve the throughput of color graphics. Even though the invention can be used in any printing environment where text and/or graphics are applied to media using monochrome and/or color comoponents, the presently preferred embodiment of the invention is used in an inkjet printer of the type shown in FIG. 1. In particular, inkjet printer 10 includes an input tray 12 containing sheets of media 14 which pass through a print zone, and are fed past an exit 18 into an output tray 16. Referring to FIGS. 1-2, a movable carriage 20 holds print cartridges 22, 24, 26, and 28 which respectively hold yellow (Y), magenta (M), cyan (C) and black (K) inks. The front of the carriage has a support bumper 30 which rides along a guide 32 while the back of the carriage has multiple bushings such as 34 which ride along slide rod 36. The position of the carriage as it traverses back and forth across the media is determined from an encoder strip 38 in order to be sure that the various ink nozzles on each print cartridge are selectively fired at the appropriate time during a carriage scan. Referring to FIGS. 3-6, a 300 dpi color inkjet cartridge 40 having a tab-circuit with a four column thirty-two pad electrical interconnect 42 is removably installed in three chutes 44, 46, 48 of a unitary carriage 50. A flex-circuit member 52 having three matching sets of conductive pads 54, 56, 58 is mounted on flex-frame pins 60 for operative engagement with the cartridge pads when the cartridge is inserted into its appropriate chute. An enlarged set of conductive pads 62 covering a larger area, having a different layout, and constituting an array of six columns totaling fifty-two conductive pads on the flex-circuit member is designed for operative engagement with cartridge pads on a 600 dpi black injet cartridge 64 (see FIG. 9). The preferred structure and techniques for preventing mistaken installation of a 600 dpi black printhead in a color printhead chute, or alternatively the mistaken installation of a 300 dpi color printhead in a black printhead chute is described in the copending applications identified above. Because of the differently configured electrical interconnect on the 600 dpi cartridge, and in order to avoid substantially changing the existing X/Y/Z datum configuration of the carriage, a unique interconnect scheme is employed. In that regard, the X-axis cartridge datums 65 engage the X-axis carriage datums 66, and the Y-axis cartridge datums 67 engage the Y-axis carriage datums 68, and the Z-axis cartridge datums 69 engage the Z-axis carriage datums 70 in a manner more fully described in the copending applications identified above. As best shown in FIGS. 9-11, a previously existing spring assembly including a backing sheet 74, a plate 76 and a gimbal spring 78 are sized for fitting into apertures 80 of flex-circuit frame 82 to assure proper electrical interconnection for the three color cartridges. Such resilient structure is described more fully in copending applications identified above. A unique spring assembly for the 600 dpi cartridge interconnect includes an unitary resilient foam member 84 which fits in a seat 86 which is larger than the aperture 80. A mounting peg 88 fits into matching hole 90 which along with bottom and lower ledges 91, 93 and upper side and top ledges 92, 94 hold the foam member in proper position to assure operative engagement across the electrical interconnect. The structure and function of the flex-circuit frame, which has been modified to incorporate the unique features of the present invention, is described more fully in copending applications identified above. FIGS. 7-8 show the preferred mounting relationship between a 300 dpi nozzle array 96 of the color printheads and a 600 dpi nozzle array 98 of the black printhead. Control circuitry 99 on the substrate enables the three hundred firing resistors of the black printhead to be controlled through fifty-two electrical interconnect pads, and similarly enables all one hundred four firing resistors of each color printhead to be controlled through thirty-two electrical interconnect pads. The multiplexing circuit scheme for such control circuitry is described more fully in copending applications identified above. FIG. 12 schematically shows the difference between the 300 dpi printout produced by the color pens (i.e., pen cartridges) and the 600 dpi printout of the black pen of the preferred embodiment described herein. Of course, it would be possible to incorporated different combinations of resolution in different printheads wherein the resolution difference may be arbitrary, depending on the printheads available and already developed, or wherein the resolution difference may be decimally related (e.g., 20% greater resolution, 30% greater resolution, etc.) or fractionally related (300dpi with 400 dpi; 300 dpi with 450 dpi, etc.). In that regard, the invention can be implemented with any of the existing inkjet cartridges which are currently available, with the best results occurring with printheads in the range of 180 dpi or greater. It will therefore be appreciated by those skilled in the art that the invention as shown and described herein allows different types of interconnects and different types of print cartridges such as cartridges of different print resolutions to be used in one product. This invention allows higher resolution and speed to occur for frequently printed features such as text and the most frequent color components of graphics such as black. Thus by printing these frequent features and components faster and at a higher resolution, the entire page is faster and of higher quality and is more comprable with laser printing performance (8+ pages per minute) and laser printing quality (600 dpi resolution). The new form of resilient interconnect member disclosed herein allows for optimization and customization for the particular contact pattern of different cartridges in the same carriage. Thus, the size of the carriage and the way that the cartridge is held in the carriage has to change very little between subsequent generations of printers. In other words, the required design change to the printer is minimized, the carriage does not have to grow wider nor taller, and the printer does not have to grow wider nor taller.

Claims: A mixed resolution printer (10) comprising: a frame for holding a media in a print zone; a carriage (50) supported on said frame to be positioned adjacent to said print zone; a first printhead (64) supported by said carriage, said first printhead having a first array of nozzles (98) extending in a substantially perpendicular direction to the direction of movement of said first printhead relative to said media for ejecting black ink droplets having a first drop size and having a first vertical print resolution; a second printhead (40) supported by said carriage in a side-by-side relationship with said first printhead, said second printhead having a second array of nozzles (96) extending in a substantially perpendicular direction to the direction of movement of said second printhead relative to said media for ejecting non-black color ink droplets having a second dropsize substantially larger than said first drop size and having a second vertical print resolution lower than said first vertical print resolution; and means (50, 41, 99) for energizing ink ejection elements in said first and second printheads such that said first printhead prints said black ink droplets at said first vertical print resolution and said second printhead prints said color ink droplets at said second vertical print resolution for composite printing by said first and second printheads on the media in said print zone. A printer according to claim 1 wherein said second printhead includes a color component selected from cyan, magenta, yellow, red, green and blue. A printer according to claim 1 or 2 wherein said first printhead has a wider printing swath than said second printhead. A printer according to claim 1 wherein said first array of nozzles has a first nozzle pitch, and said second array of nozzles has a second nozzle pitch, with said first nozzle pitch less than said second nozzle pitch as measured in a media advance axis. A printer according to any preceding claim wherein said first and second printheads are mounted in said carriage in relative positions along the media advance axis in order to produce at least partially overlapping print swaths from said first and second printheads. A printer according to any preceding claim wherein said second printhead is mounted in said carriage to be in completely overlapped printing alignment with said first printhead. A printer according to any preceding claim wherein said first printhead prints at a resolution of 600 dots per inch and said second printhead prints at a resolution of 300 dots per inch. A printer according to any preceding claim further comprising a third printhead (22) and a fourth printhead (24) supported by said carriage, said third and fourth printheads being identical to said second printhead, but printing different colors of ink. A printer according to any preceding claim wherein said first printhead is mounted in a print cartridge separate from a print cartridge in which is mounted said second printhead.

Inventors: AZMOON MAJID, HARRIS DONALD G, NOBEL GARY M, AZMOON, MAJID, HARRIS, DONALD G., NOBEL, GARY M.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1994
Main classification: B41J2
IPC codes: B41J2, B41J3, G06K15